1. Field of the Invention
This invention relates to an apparatus and method for adjusting the camber of land vehicle wheel assemblies. In particular, it relates to a unique shim, and a method for installing the shim into the wheel assembly of a vehicle whereby wheel camber and the position of the brake caliper are adjusted together so that camber adjustment does not adversely affect the brake system.
2. Description of the Prior Art
The wheels of automobiles and other land vehicles must be properly aligned to reduce tire wear and to provide a true, free-rolling movement over the road. Wheel alignment is typically described in terms of camber, toe, caster, turning radius and steering-axis inclination. Caster, turning radius and steering-axis inclination are designed-in features, and are generally not subject to adjustment after a vehicle has been manufactured. Camber and toe, however, are subject to close tolerances that are difficult to achieve during manufacture and that require adjustments over the life of a vehicle.
Camber is a measurement in angular degrees of the inward or outward tilt of a wheel as measured from a vertical plane. Camber is usually considered "positive" when the top of the wheel leans outwardly towards the side of the vehicle, and is considered "negative" when the top of the wheel leans inwardly. In other words, two wheels that are at opposite ends of a common axle have positive camber when the tops of the two wheels are further apart from each other than the bottom of the wheels.
Incorrect adjustment of camber can lead to rapid and excessive tire wear, adverse handling of a vehicle, and rapid deterioration of the bearings supporting the misaligned wheel. Camber must be optimally set at the factory after assembly of a vehicle. Moreover, camber should be inspected and adjusted after operation of a vehicle over rough roads, involvement of the vehicle in an accident, and during routine maintenance checks.
U.S. Pat. No. 4,037,680, issued to one of the named inventors of this application, discloses an annular, tapered shim that is placed between the respective mounting pads of the spindle of a wheel and the axle to which the wheel spindle is attached. As disclosed in U.S. Pat. No. 4,037,680, different shims, each having different amounts of taper, can be placed between the wheel spindle and its supporting axle in this type of wheel assembly to selectively adjust the camber of the wheel. Locating the point of maximum thickness at the top of the installed shim yields a camber adjustment equal to the angle of taper. The shims include a plurality of apertures such that the bolts holding the wheel spindle to the axle can be received through the shim. A somewhat similar shim is shown in U.S. Pat. No. 4,195,862.
While prior art shims have had a variety of bolt hole configurations to allow them to accommodate different configurations and locations of fasteners connecting axles and wheels (see, e.g., U.S. Pat. No. 4,684,150), recent wheel suspension designs have led to new wheel assembly designs and have introduced a problem that cannot be accommodated by these known shims. In certain newer model cars, MacPherson strut suspensions are used. These suspensions have a housing at the lower end of the strut. On the housing is a mounting plate that is used for mounting both the disk brake caliper and also the hub and wheel bearing assembly associated with the wheel at that suspension assembly.
In this type of suspension, it is desirable to adjust camber by changing the angle between the mounting plate and the associated hub and wheel bearing assembly. A shim of conventional type might be used for this purpose. The difficulty with this is that adjustment using a shim at this location unavoidably affects the angle of the brake rotor (which is mounted on the hub and wheel bearing assembly). When the angle of the brake rotor is changed, it is no longer aligned with the brake caliper (which is mounted on the mounting plate). Although the angular misalignment and physical displacement may be relatively small, the brake system is still adversely affected. Accordingly, a shim that would permit camber adjustment in this type of suspension environment while preserving alignment between the brake rotor and brake caliper would be highly desirable.